Process of working glass



Patented Nov. 10, 1953 2,658,317 PROCESS OF WORKING GLASS Willard L. Morgan,

Pittsburgh, Pa., assignor to Libbey-Owens-Ford Glass Company, Toledo,

Ohio, a corporation of Ohio No Drawing. Application February 23, 1951, Serial No. 212,503

8 Claims.

This invention relates broadly to a process of working glass and is more particularly concerned with the grinding of the edges of the glass or the grinding of surfaces of glass in which some surfaces are being worked upon while others are not.

The invention is further concerned with such operations wherein a cooling fluid, such as water and emulsified oil, is applied to the edging wheels or grinding tools during such work. During such abrading operations, extremely fine particles of glass are continuous removed and these very fine particles are found to be directly soluble to some extent in the water in the cooling fluid. Such solution rapid becomes alkaline where the fiuid is reapplied and reused in a cyclic manner upon the grinding machines. The alkaline solution thus generated is deleterious upon the other surfaces which are not being worked upon and results in etching and loss of finish upon such surfacesf also concerned with the procarticles having a glass face laminated glass. In the case desirable to bevel or other- The invention is essing of completed such as mirrors and of mirrors where it is wise finish the edge of ing upon one face the mirror film and protective paint backings, it has been found that severe losses due to etching of the uncoated face of the mirror oftentimes results where the mirror edge i being ground by high speed diamond wheels and the cooling lubricant is continuously recycled to such wheels. Likewise, in the grinding of surfaces of optical elements such as prisms, for example, the finishing of successive faces under such circumstances has been found to result in articles which are defective in that the first finished faces are found to be etched due to contact with the fluid during the later treatment of other faces.

In accordance with this invention, it has been found that the above difficulties may be obviated and continuous high speed production machines may be run without encountering such difficulties by the addition of an acid reacting material such as boric acid to the system in which the cooling fluid recirculates. The boric acid reacts with any alkaline condition present in the coolant and reduces the same or creates a slight acid condition, either of which results in cooling fluids which do not etch glass surfaces. Boric acid is particularly effective for this purpose in that, unlike some other acids, it may be added in excessive quantities without any effect upon the glass surfaces or the machines, thus eliminating any requirements as to determining an exact the completed mirror havbecomes only necessary in boric acid such as but preferably weak acids such as boric acid,

amount to offset the alkalinity present. This is particularly useful since the alkalinity developed in the cooling fluid varies with the amount of glass which has been worked and the total time that the machine has been operated. Thus, it the use of boric acid to know that there is an excess of boric acid present in the coolant.

The present invention comprises the additional feature of placing in the cooling fluid a dyestuff or other material which has the properties of changing color in the presence of harmful alkaline conditions. Specifically, the material phenolphthalein is added to the coolant in the form of an alcoholic aqueous solution such as 1% solution in 50% alcohol, and if the solution is harmfully alkaline, it will be indicated to the operator by the solution turning a bright red color. In the'presence of excess or free boric acid, the red color from the phenolphthalein is destroyed and the solution becomes colorless. Thus, the operator of the machine is automatically told by the development of the pink color when to add more boric acid to the operation.

Other acids can be employed in place of the hydrochloric or sulfuric acid,

oxalic acid, lactic aid, benzoic acid, acetic acid, phthalic acid, phosphoric acid or, more desirably, the acid sodium, potassium, or ammonium phosphates, are used. It is preferred, however, that boric acid or the acid phosphate salts be employed since these are of a nature such that their acidity is so weak that they have no corrosive action upon the machinery when used in excessive amounts, and they further are free of any harmful action upon the skin or clothing of the operators who are subject to contact with the fluid directly during the placement of the work in the machine and its removal therefrom. These last-mentioned materials are also desirable by reason of the fact that they are also solids and the handling of them by the operator is thus very simple. While hazards may thus be involved in the use of the stronger and also liquid acids, it is obvious that these can be employed, and it is merely desirable in such cases that a color changing material be present in the continuously recirculated cooling fluid to signalize to the operator by one color when acid is needed and to signalize by another color when sufficient acid has been added.

Other dyestuffs or so-called indicating materials which may be employed in place of phenolphthalein are methyl red, neutral red, brome beveling and/or grinding operations within a hydrogen ion or pH condition of lessthan 8.5 and preferably above 4, and with the'in'cl'us'lon generally in such fluid of an indicating 'material showing by color changes when the tluid becomes more alkaline than the upper pH of 8.6.

By the use of a combination .of.phenolphtha1ein and methyl orange jointly in the circulating fiuid, the two dyestufis will automatically indicate the holding of the acid or alkaline conditions within the rangeof pH 4 to 8.5 by color changes. Thus, if 'the pH exceeds 8.5, the :solu- 'tion would be red or-p'inkish due' to-theiphenolphthalein. In the range of '4 to 8.5, the "solution would have a slight yellow tintdueto the methyl orange and due to the .fact that the 'phenolphthalein is colorless .in such range. At

pil s below 4, thesolutionagain wouldhave a red color, but this time due to ithe'fact-that the methyl orange producessuch redwhile thenhenolphthalein is still colorless. Such a combination of indicators =in the circulating fluid would permitthe use and addition of any acid material to secure and maintain the solution within this desired range. Specifically, using methyl red'asa singleindi'cator, thlsmaterial is known to change from a red the hydrogen ion condition '6. With brome 'c'nesol purple, the color goes from a yellow to a purple-when thesolution'cx- Ito'a :yellow when begins to exceed pH ceeds a pH of "7., and with the brome 'thymol blue the solution becomes blue and: changes from yellow'whe'n the condition of the fluid exceeds pH 7.5. Specifically, however, phenolphthalein or th'ymol blue which changes from a blue to a yellow at pH 8.5 are,.gcnerally speaking, the-pre- 'ferred indicators where the acids :h'erein iprovided are employed and particularly where boric acid orthe acid sodium phosphates such asmonosodium or disodium hydrogen phosphate are used.

In the continuous use of high "speed edging,

be'veling and grinding machines in which the coolanttluid is recirculated, a veryconsiderabie amount 'of finely divided-glass-is-produced which an extreme amount of surface. From such fine glass material, there is .a directsolution 1 out of the some and-into the'aqueouscoolant of alkali as sodiumhydroxide and caiciumhydroxidaand also-a solution of alkali and silica-as sodium silicates. These dissolved sodium'silicates "as well as the alkaline hydroxides are strongralkaline matienials. This can-bedirectiy demonstrated by mixing powdered glass-into: water and very quickly 'it will be found that the solution :be'colnes strongly alkaline. Thus, within twenty minutes after adding-such powdered glass-towater which was neutral, namely, of a pH or hydrogen ion condition of "7, the azlkalinity'was found to be 9.1, and after twenty-four hours the alkalinity was-found to be pH'11.1. Onpouring on such water andrepeated-by leaching -such..-glass with further additions of'water,

it will be found that alkali continuously dissolves away from the glass. Even after ten washings, whenthe glass is left twenty+four hours each time in the water. the .PH will be foundto rise to 10.2 toflllrl.

formed by'adding -1 'mineral oil to a gallon of water was found to 'ing-to the skin of the glass lass causes some The following table gives data on the successive repeated washings with equal quantities of water of the same sample of powdered glass:

Number of Washes 5353 pH .The results are typical and the pHs might be higher if a large ratio of powdered glass to water were employed. It clearly shows, however, that alkali dissolves from the glass and, secondly. that alkali continuously dissolves away from the glam even over long periods of time. Such solutions-prepared by dissolving powdered glass in 'wa'terhave been found to directly etchglass mfwces when applied 'to'thesame and when those are of apH of over 8.5.

A coolant employed in edging glass that was ounce of ,a selfemulsifying have a pH, when'mixed, of 7.9. When this was charged into a clean glass grinding machine usedfor beveling glass whereit was continuously recirculatedthe fluid wasfound to-have changed very :quickly after the beveling of only twenty rear view automobile mirrors to -a,pH:oI 8.85. This was after bovcling only .760 lineal inches. and'at'terfour sueh machinm hadbeen runior four hours-continuously, thecoolant was round tobe inan alkaline condition ineolch-oi'a pH of 9.3, 9.9, 10.0, and 10.7, respectively. After running these machines for two weeks. the pH values were up to 10.2, 10.4,.10.6, and 11.1, respectively.

These trongly alkaline solutionsas taken from the circulating machines were found'to etch the exposed unooated surfaceof the mirrors or of glass-plates'to'which such solution was applied.

The strongly alkaline solutions were also irritatworkers and ate thmugh various-types of paint appiiedito the mirror back.

:causingadditional rejections due to such action through'the paint and destroying the silver film. Spoilagcs of ten to twcnty'percen't under such conditionsin the working of'rcar view automobile :mirrors were commonly eiqcerienoed and have been avoided'by the methodsof thie invention.

Under continuous use of such beveilrg .mechines, a very. large amount of veryflnelygcound gaccmnulate in the rcirculatim systanzond in particular settles out in the supply this 'and other paristot'themadzme where flcejuid motion isnotraoi'xi. This heavy *siuckeot finely diflded'glass rsettia in 'a very. hard and'wmpnct mass and approaches a-cement-likle hard roan aftero few days use which isextremely mat to remove fromthe machinery. Apparently the slow solution of alkali from the surface of the sort of rcaction'withadiacent glass-particles resulting in a cementing of the same together,-.pmbably through the local tarmation of a heavy concentration of alkali silioatm.

One of theuoth'er advantages 'ofthe invention is that when the circulating cooling fluid is maintained within a pH range of less than 8.5 and particularly where boric acid is-employed, the sludgedoes notsettleinto a hard mass but, in-

stead, settles in a very soft dispersed condition which permits easy flushing of the sludge from the machinery. Thi results in very large savings in maintenance and cleaning of the machines.

By way of contrast to the figures given above which show the development of alkali when continuously beveling glass with a recirculated cooling fluid, the following data shows how, by the use of phenolphthalein indicator and boric acid in the beveling solution, the hydrogen ion condition was kept well Within the desired range of less than 8.5.

More specifically, the coolant fluid comprised a solution of 1 gallon of water, 1 ounce of selfemulsifiable mineral oil, /15 ounce of a one percent phenolphthalein solution in fifty percent alcohol. To the machine, 1 pound of boric acid was added after the zero time reading was made. In the following table it is apparent that the machine was operating under a strongly alkaline condition before the boric acid was added as shown at zero time, and under such condition the solution was bright red due to the phenolphthalein, indicating the presence of such alkali. When the boric acid was added, the solution progressively and quickly lost the red color through gradual shades of pink and became colorless within a few minutes. It will be seen that after one-half hour, the machine was operating in a satisfactory pH range of 7.95 and that this was readily maintained over an extended period by the use of boric acid.

- Time in Hours After Adding Boric Acid pH 1 Acid not added.

2 Acid added.

In the running of this test, 1 pound of boric acid was added at the end of each twenty-four hours, and the machine was beveling approximately 60,000 lineal inches per day. In such trial where there had been a nine percent of mirrors processed in the machine before the addition of the boric acid, the rejections due to etching of the face of the mirrors and due to spoilage of the mirror film by alkali attack through the protective paint backings were completely eliminated after the boric acid was added to the machine.

In a similar manner Where glass prisms were being surfaced using a cooling fluid comprising mostly water and a small amount of emulsified mineral oil, and in which the two finished faces of the prisms were exposed to the coolant during the grinding of the third face, it was found that by the addition of phenolphthalein indicator and boric acid to the circulating fluid system, the re jections due to attack on theglass faces and etching of the same by the circulating fluid were eliminated.

In these operations, boric acid, due to its solid nature, showed to very excellent advantage, resulted in no complaints from the operating personnel, and offered the further advantage that the exact quantity to be added at any time did not have to be predetermined but that any amount might be added to the system provided sufficient was added to destroy any red or pink color and loss of approxinriately,

thereby bring the pH'within the desired range of less than 8.5. As boric acid is a material of relatively low water solubility, it has the further advantage that excessive amounts may be added right into the system and the solution of such into the cooling fluid occurs slowly and as needed to offset the alkali being developed by the solution of the glass. Thus, in a sense the limited solubility of boric acid acts to advantage in providing a simple supply mechanism within the fluid. Consequently, no special control is needed in the application of the invention and any unskilled workman can be relied upon to perform the method satisfactorily.

As the above table will indicate, the pH in the system employing boric acid does not fall down within an acid range to any large degree, and it will be recognized that a further function which makes the use of weak acids desirable is that such weak acids, after they react with the alkali present, set up what are known as buffer conditions. That is, the range of pH of the mixture of boric acid and of alkali borate formed by reaction with the alkali falls within fairly narrow ranges, and it is for this reason that the range of pHs shown in the above table of data taken upon the machines falls within the narrow range ofpH 7.7 to 8.2. This buffering mechanism functions excellently to permit long time continuous use of the beveling or grinding machines without recleaning, since the more sodium borate which is formed, the more the buffering action becomes apparent. Thus, it has become possible to run such machines continuously for several weeks, the only limiting factor being the accumulation of total ground off glass.

It will also be apparent that where a salt of a weak acid such as sodium borate or a sodium phosphate is added to a circulating cooling fluid and an indicating material is also added, the weak acid may be generated right within the coolant by the subsequent addition of another or stronger acid. Thus, the advantages of employing boric acid could also be secured by the addition of ordinary borax along with phenolphthalein and the addition to the solution, whenever it became too alkaline as shown by red color development, of a strong acid such as hydrochloric or phosphoric acids, for example. These strong acids would liberate boric acid within the solution and thereby secure the benefits directly attainable by the use of such. It is obvious of course also that the use of weakly alkaline and weakly acid salt combinations or buffer mixtures may be employed as the source of acidity to be added to the circulating fluid, the proper conditions in any case being indicated through the use of an indicator in the circulating fluid. The invention thus comprises maintaining the circulating fluid within a pH range of less than 8.5 and preferably of over 4 as signalized and indicated by the presence of color changing substances in the fluid and the addition to the fluid of an acid reacting material or other substances which will keep the pH below the desired 8.5. It is apparent that the invention may also be practiced by adding the acids or acid reacting substance to the coolant while maintaining the pH in the desired range of 4 to 8.5 by tests made upon samples of coolant which might be taken from the circulating system. These tests might be made with the indicator color changing materials, or papers containing such, or by well known electrical hydrogen ion or pH determining instruments.

acumen 7 It will be apparent thatthe acids "functlonto destroy the sodium hydroxide, the calcium hydroxide, and the corresponding alkali zsi-licates which dissolve from the finely ground glass particles by reacting with the same and forming the corresponding alkali salts of such acids. Thus, when boric acid is employed, the sodium hydroxide and silicates would be changed 130 sodium borate and it hydrochloric acid were used.then sodium chloride would be'formed. It. is apparent rrom the well known bufiering actions of salts of weak acids thatthe weak acids offer advantages over the use of the stronger acids. It is also obvious that acids of an organic nature may be employed, such as oxalic, benzoic, and phthalic acids. With the exception of higher-cost, the last two offer many of the advantages found with boric acid.

I claim:

1. In the process :of working glass, the steps of removing small particles of glass from the main body, applying and recirculating a fluid aqueous cooling media to the area of working during the removal of said particles,-and adding an acid reacting material to said cooling media in-sufllcient quantity to maintain-the pH of a solution of the glass particles in the cooling media at a value of less than 8.5 and over 4.

2. In the process of-working glass, the steps of removing small par-ticles'of glass from the main body of the glass, applying and recirculating a fluid aqueous cooling media in which said particles are soluble to the area of working during the removal of said particles, and adding an acid reacting material to solution of glass particles and cooling media in sumcient quantity to maintain the pH of said solution at a value of less than 8.5 and over 4.

3. In the process of working glass, the steps of removing small particles of glass from the main body, applying and recirculating .a fluid aqueous coolingmedia to the area of working during the removal of said particles, adding to the cooling media an indicating material .characterized by a visual change in color when the pH exceeds 8.5 or is less than 4, and further adding an acid reacting material to said cooling media in suflicient quantity to maintain the pH oi. a solution of the glass particles in the cooling media within said range.

4. In the process of working glass, :the steps of removing small particles of glass from the main body'thereof, applying and recirculating a solution of aqueous cooling media comprisingan acid reacting materialto the area otworking during the removal of mid partieles, and adding said acid reacting material to said solution .m sumcient quantity to maintain the pH thereoi. at a value not exceeding 8.5.

5. the process or working glass, the steps of removing snail particles of glass from the main body thereof, applying and recirculating .a solution of .fluid aqueous cooling media comprising an acid reacting material and a color changing material characterized by a visual chame in color when the pH exceeds 8.5 or-is less than '4 to the area of-working during the removal .01 said particles, and adding said acid reacting matm'ial to said solution in sumclent quantity to maintain the pH thereof within said-range.

5. In 'theprocess of working glass, the steps of removing small particles of glass from the main body thereof, applying a fluid cooling media including a color changing material characterized bye visual change in color when the pH exceeds 8.5to the main glass body during the removal of saidparticles, and adding boric acid to a solution of theglass particles in the cooling media when the pH of said solution is observed to exceed 85.

7. In the process of working glass, the steps of removing small particles "of glass from the main body'thereoi', applying and recirculating .a fluid cooling media including a color changing material characterized by a visual change in color when the pH exceeds 8.5 to themainglass body during the removal of saidparticles, and adding bor-ic acid to a solution-of the glass particles in the cooling media when the pH of said solution isobserved --to exceed 8.5.

8. In the process or working glass, the steps zmain glass body during the removal 0! said parchange'oi the presence of boric acid in free unreacted form.

WILLARD L;

References Cited in the file 0! this patent UNITED STATES PATENTS Number Name Date 2,366,825 Adams Jan. 9, 1945 2,387,142 Fruth Oct. 16, 1945 v2,390,405 Walker Dec. 4. 1945 

